[llvm] [DAGCombiner] Freeze maybe poison operands when folding select to logic (PR #84924)

[Björn Pettersson via llvm-commits]

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@@ -6,21 +6,14 @@
 
 ; (x0 < x1) && (x2 > x3)
 define i32 @cmp_and2(i32 %0, i32 %1, i32 %2, i32 %3) {
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bjope wrote:

I guess the typical problem here is that the arguments aren't marked as `noundef`. But even if they had been marked as `noundef` the lowering of arguments wouldn't resulting adding FREEZE nodes to indicate that the inputs aren't poison. Nor do we have a way to put such attributes on the CopyFromReg (or loads from stack) instructions that would map to accessing the arguments.

(No idea if there  is something in AArch64 that could be changed here to still optimize this in a valid way or if the old transform is unsafe from a poison/undef perspective.)

https://github.com/llvm/llvm-project/pull/84924